You have to rent your tux before your cruise - you cannot book it on board.

This is the info I got from HAL's website underPLANNING & ADVICE

Clothing & Dress Code

Formalwear for ladies and gentlemen can be pre-ordered for your use during your cruise by calling Cruiseline Formalwear at 800-551-5091 or make your reservations online. Your formalwear will be in your stateroom when you board. Cruiseline Formalwear Packages

I believe that any alterations that need to be done can be made on board by the tailor.